In recent years, networking of offices, as well as digitalization and colorization of handled documents have advanced.
The digitalization has facilitated document processing and transfer, and streamlining of business has been attempted.
Moreover, beautiful looking and effective documents have been generated through the colorization.
While such digitalization and colorization of the documents have advanced, effective capture and output performance for generated image data is required in a multifunction peripheral which is an image processing apparatus.
A configuration of a reader in the multifunction peripheral which inputs the image data is an element which is most related to capture of original document image data or image quality of output images at the time of a copy operation.
As the configuration of the reader in the multifunction peripheral, there are a reduction optical system and a contact optical system.
Reading resolutions of these optical systems depend on sensor components for a pixel arranged in a primary scan direction.
As a process of improving the resolution without depending on the number of these sensor components for a pixel arranged in the primary scan direction, there is a technique referred to as “super-resolution processing”.
Although this technique will be described later, the super-resolution processing uses a plurality of frames of the image data read at the resolution of the sensor included in the reader. Therefore, a resolution of the output image is dramatically improved.
Usage of the super-resolution processing technique enables, for example, generation of image data with a resolution of 1200 dpi by using a plurality of pieces of image data read at a resolution of 300 dpi.
International Publication No. WO 2004/068862 describes details of processing contents of the super-resolution processing in which high resolution image data which cannot be obtained by the reader is generated from the plurality of pieces of the image data.
Moreover, Japanese Patent Application Laid-open No. 2006-092450 describes realization of high resolution processing by controlling the number of images which are sources of a synthesized image depending on an image size.
This control is performed so that the number of frames to be synthesized is increased for a smaller image size.
However, in order to perform the above described super-resolution processing, first, a plurality of frames of the image data is required in which an original document image reading position has been shifted by a very small amount, with one frame image read at the resolution of the sensor included in the reader, as a reference.
In other words, a plurality of continuous frames of the image data is required in which a position of an original document read by the sensor has been shifted from reference image data, little by little in the primary scan direction and/or a secondary scan direction.
Moreover, when this plurality of pieces of the image data is read, the shift in the original document image reading position exists among the image data obtained by adjacent sensors. This shift is required to be less than one pixel (sub-pixel) in the primary scan direction and/or the secondary scan direction.
The higher the resolution of the image data to be generated by the super-resolution processing is, the larger the number of necessary frames of the image data read at the resolution of the sensor included in this apparatus is.
If the super-resolution processing can be performed in the multifunction peripheral, a high resolution image which would be realized with a high resolution reading device can be obtained with a low resolution reading device, which, however, requires satisfaction of conditions as described above.
However, line sensors are generally used in the reader in the multifunction peripheral, such as a scanner in the multifunction peripheral.
In other words, the number of read frames which can be obtained in one reading operation is one frame.
Moreover, the above described reader reads an original document image by using a group of the sensor components for a pixel which are arranged horizontally in the primary scan direction at a distance of an integral multiple of a pixel.
Consequently, there is a problem in that a position of the pixel to be read cannot be shifted by a very small amount (sub-pixel) in the primary scan direction to read the original document image.